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Types of tunnel supports and necessity

Short answer

Types of tunnel supports: rock bolts (grouted/friction), shotcrete with mesh/fibres, steel ribs with lagging, cast-in-place concrete lining, wire mesh, and pre-support like forepoling/pipe-roof. Their necessity is to stabilize the opening, prevent rock fall, control deformation and water inflow, and carry load until permanent lining is installed; selection depends on rock quality.

Discuss with sketches the types of tunnel supports and their necessity.

Types of tunnel supports

  Rock bolts          Steel rib          Shotcrete + mesh
  \  |  /          ___________            ___________
 --\ | /--        /  ribs +   \          / sprayed  \
  /-+-+-\        |  lagging    |        | concrete    |
 /  | |  \       |             |        |   layer     |
  1. Rock bolts: steel bars (fully grouted or friction type) 2-5 m long, installed in a pattern. They bind the loose blocks into the sound rock and form a reinforced ring.
  2. Shotcrete: sprayed concrete (with mesh or fibres) that seals and supports the surface.
  3. Steel ribs/arches: I-section or lattice girders, with lagging (timber or steel plates) or shotcrete in between; used for weak rock and fault zones; closed rings used for squeezing ground.
  4. Concrete lining (plain or reinforced; cast-in-place or precast): the permanent support.
  5. Wire mesh and forepoling / spiling / pipe-roof (pre-support) ahead of the face in very weak ground.
  6. Timber supports for small, temporary works (rarely in large tunnels).

Necessity of supports

They keep the opening stable and safe, prevent fall of rock, control deformation and water inflow, and carry the load until the permanent lining is placed. The type is selected by the rock quality (Q-system/RMR): sound rock needs little or no support, jointed rock needs bolts and shotcrete, and poor rock needs ribs and pre-support.

✓ Answer checked by Claude Opus 5.5 (high effort)

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